It is known to prepare castings from hyper-eutectic aluminum-silicon alloys. Such alloys have from 12.5 to 25.0 percent by weight of silicon and have better strength and ductility than those made purely from aluminum. Consequently, they exhibit better wear resistance than those with lower silicon content. The exceptional wear resistance of the alloys make them suitable for casting heavy duty parts such as automotive engines and pistons. Castings from such alloys are prepared by conventional means by pouring a molten alloy mixture into a core or pattern mold and allowing it to harden. The casting is then removed.
If the castings are to be acceptable they must not contain significant defects in the grain of the casting. Such defects result from impurities in the aluminum-silicon alloy such as hydrogen and oxides. They also result because the primary silicon particles may agglomerate with the result that they enlarge and are not uniformly distributed in the casting.
These defects in the castings can cause the casting to be brittle, and to have weak and strong areas in the grain. Consequently, the castings may chip or break during machining. Reduced machine tool life and down time are also likely to result.
Therefore, it is important to reduce or eliminate impurities and refine primary silicon particles in the molten aluminum alloy in order to enhance the physical properties and machinability of the castings.
Generally, impurities such as those mentioned, are removed from the aluminum-silicon alloy in separate steps. Usually the hydrogen gas is removed followed by the removal of oxide impurities. Then the silicon is refined with phosphorus to prevent it from agglomerating.
The standard method is time consuming and often inefficient. It would be more efficient to reduce the steps involved.